Field of the Invention
The present invention relates to an ultrasonic cleaning apparatus for cleaning workpieces to remove burrs, foreign matter, or the like from their surfaces by immersing the workpieces in a cleaning solution in an ultrasonic cleaning tank and radiating ultrasonic energy into the cleaning solution, and more particularly to a pressurized ultrasonic cleaning apparatus for ultrasonically cleaning workpieces immersed in a cleaning solution in an ultrasonic cleaning tank while the cleaning solution is being pressurized.
Description of the Prior Art
Heretofore, there have been known ultrasonic cleaning apparatus for cleaning workpieces to remove burrs, foreign matter, or the like from their surfaces by supplying a cleaning solution to an ultrasonic cleaning tank with an ultrasonic vibrator mounted therein, immersing the workpieces in the cleaning solution, and radiating ultrasonic energy into the cleaning solution.
When the ultrasonic energy is radiated from the ultrasonic vibrator into the cleaning solution, the cleaning solution is cavitated, and the workpiece is exposed to shock waves or microjets that are produced when the cavitation is collapsed. Foreign matter or burrs can be removed from the workpiece by those shock waves or microjets. For efficiently cleaning workpieces, it is necessary to provide conditions which facilitate the generation of the cavitation in the cleaning solution.
As a result of an analysis of those conditions, the inventor has found out that the cleaning solution can be cavitated more easily if the concentration of a gas dissolved in the cleaning solution is lower, and that if the concentration of a gas dissolved in the cleaning solution is too high, then the dissolved gas is converted into bubbles by the ultrasonic energy radiated by the ultrasonic vibrators, making the cavitation less susceptible to collapsing. Furthermore, since the ultrasonic energy is absorbed by the bubbles, the microjets are weakened by the bubbles. Therefore, when such bubbles are produced in the cleaning solution by the dissolved gas, the cleaning of the workpiece is essentially carried out only by the bubbles, but not by the ultrasonic energy.
The inventor has also found out that the cleaning solution can more easily be cavitated when the cleaning solution is deaerated and subjected to a suitable static pressure, and has proposed an ultrasonic cleaning apparatus which applies a static pressure to a deaerated cleaning solution while a workpiece immersed in the deaerated cleaning solution is being ultrasonically cleaned (see Japanese patent publication No. 4-46637).
As shown in FIG. 4 of the accompanying drawings, the proposed ultrasonic cleaning apparatus includes an ultrasonic cleaning tank 61 having a tank body 64 supplied with a cleaning solution 63, an ultrasonic vibrator 62 mounted on the bottom wall of the tank body 64, and a lid 66 which sealingly closes the tank body 64 when a workpiece 65 is immersed in the cleaning solution 63 in the tank body 64. The lid 66 is vertically movable by a cylinder 67 to open or close the tank body 64. An air conduit 69 having an air bleeder valve 68 is connected at a lower end thereof to an upper end of the lid 66.
The tank body 64 has a cleaning solution inlet 70 disposed on a side wall thereof. When the ultrasonic cleaning tank 61 is completed by the tank body 64 and the lid 66 that sealingly closes the tank body 64, the cleaning solution 63 is supplied from the cleaning solution inlet 70 to fill up the interior space of the ultrasonic cleaning tank 61. The cleaning solution inlet 70 is connected by a cleaning solution conduit 71 to a cleaning solution outlet 72 disposed on the side wall of the tank body 64 in diametrically opposite relation to the cleaning solution inlet 70. Specifically, the cleaning solution conduit 71 is connected to the cleaning solution outlet 72 through a flow control valve 73a and the cleaning solution inlet 70 through a flow control valve 73b. The cleaning solution conduit 71 is connected to the flow control valve 73a through a deaerating device 74 for deaerating the cleaning solution 63, a pump 75 for drawing the cleaning solution 63 from the cleaning solution outlet 72 and supplying the cleaning solution 63 to the deaerating device 74, and a filter 76 disposed upstream of the deaerating device 74 for removing foreign matter contained in the cleaning solution 63.
A pressurizing cylinder 78 with a piston 77 is mounted on the side wall of the tank body 64. The pressurizing cylinder 78 serves as a pressurizing means for applying a static pressure to the cleaning solution 63 in the ultrasonic cleaning tank 61.
In operation, the closed ultrasonic cleaning tank 61 is filled up with the cleaning solution 63 that has been deaerated by the deaerating device 74, and the cleaning solution 63 in the ultrasonic cleaning tank 61 is pressurized under the static pressure applied by the piston 77 in the pressuring cylinder 78. Therefore, the proposed ultrasonic cleaning apparatus can easily achieve the conditions for facilitating the generation of the cavitation in the cleaning solution 63 to clean the workpiece 65 effectively.
The pressuring cylinder 78 is subject to large forces applied to pressurize the cleaning solution 63, and is directly coupled to the ultrasonic cleaning tank 61 through a relatively large opening. While the workpiece 65 is being ultrasonically cleaned, therefore, the pressuring cylinder 78 is exposed to intensive shock waves or microjets produced upon collapse of the cavitation developed in the cleaning solution 63. Particularly, the junction between the pressurizing cylinder 78 and the side wall of the tank body 64 tends to be broken by those shock waves or microjets. Since a portion of the ultrasonic cleaning tank 61 itself is used as a pressure cylinder, once the tank body 64 is broken, it is highly difficult to repair or restore the tank body 64. Usually, the broken tank body 64 and the pressurizing cylinder 78 coupled thereto must be replaced with a new combination.